Automatic ladling control for metal melting furnace



Dec. 17, 1957 E. w. EDSTRAND 2,816,334

AUTOMATIC L ADLING CONTROL FOR METAL MEL-TING FURNACE ed Sept. 24, 195642 I19: 1.

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United States Patent AUTOMATIC LADLING CONTROL FOR METAL MELTING FURNACEElmer W. Edstrand, Berkeley, lll., assignor to Lindberg EngineeringCompany, Chicago, 111., a corporation of ois Application September 24,1956, Serial No. 611,419

12 Claims. (Cl. 22-79) This invention relates generally to metal meltingfurnaces and more particularly to an automatic ladling control for metalmelting. furnaces.

Metal melting furnaces are known in the prior art wherein a charge ofcold metal is heated to a molten state or is held in a molten state byelectric induction, fuel combustion and the like and the molten metalre-' sulting from the heating is removed from the furnace by means of apump associated with the furnace. Advantageously, the pump may be of thetype which is seated over the open upper part of the furnace and whichcauses the molten metal to be discharged through a suitable. dischargechannel connected to the pump byapplying gas pressure to the surface ofthe molten metal. Inasmuch as the discharge channel generally extends asubstantial amount into the molten metal within the furnace it has beenfound that the amount of molten metal discharged by the operation of thepump for a set time varies in accordance with the level of the moltenmetal within the furnace. Manifestly this condition is a whollyunsatisfactory one as it is desirable in a large number of applicationsthat a uniform amount of molten metal be discharged for every operationof the pump.

Accordingly, it is a general object of this invention to provideimproved meansfor controlling the discharge of molten metal from afurnace.

More specifically it is an object of this invention to provide animproved control circuit which compensates for variations in the levelof molten metal within a furnace to discharge a predetermined amounttherefrom.-

It is another object of this invention to provide an improved ladlingcontrol for a metal melting furnace which automatically enables thedischarge ofa uniform amount of metal therefrom regardless of the levelof the metal within the furnace.

It is a further object of this invention to provide elec' tronic meansresponsive to the quantity of molten metalin a metal melting furnace forcontrolling the amount of molten metal discharged therefrom.

It is a still further object of this invention to provide an improvedcontrol circuit for automatically determining the period of operation ofa discharge pump associated with the furnace.

It is a still further object of this invention to provide such animproved automatic ladling control for metal.

ing the discharge of molten metal therefrom. The period. of time duringwhich the pump operating valve is en-' ergized is controlled by a novelelectronic circuit having a discharge device which is maintainednonconductive;

for the desired length of time after the discharge opera-1:

tion is initiated.

2,816,334 Patented Dec. 17, 1957 The dischargedevice is held in normallynonconducting condition by a bias potential applied thereto. The controlfurther comprises a float adapted to be placed in the molten metalwithin the furnace crucible such that its level varies in accordancewith the level of the molten metal. The float is connected to apotentiometer wiper which provides an output voltage that varies inaccordance with the position of the float. The potentiometer outputvoltage controls the magnitude of the bias potential applied to thedischarge device, which potential is removed when the pump operation isimtiated. Thus, the position of the float, i. e., the level of themolten metal in the furnace crucible, determines the period of timeafter removal of the bias voltage, before the discharge device becomesconductive and stops the pump.

Therefore, it will be understood that for relatively high levels ofmolten metal within the furnace crucible the bias potential on thedischarge device will be such as to cause it to become conductive arelatively short period of time after the pump is started and converselyfor low levels of molten metal within the furnace crucible thebiaspotential on the discharge device will be such as to cause it tobecome conductive a relatively long period of time after the pump isstarted. Since the energization of the pump operating valve fordischarging the to' insure that an equal amount of molten metal isdisspecification. For a better understanding of this invention, however,its advantages and specific objects attained by its use reference is hadto the accompanying drawing and descriptive material in which is shownand described an illustrative embodiment of the invention. 7

In the drawing:

Figure 1 shows a metal melting furnace of a type embodying the presentinvention; and

Figure 2 is a schematic diagram of the electronic control circuitryembodying the invention.

Referring now to the drawing and more particularly to Figure 1 there isshown a dual chamber type induction furnace with which the inventionadvantageously may be used. The furnace as shown comprises a main body10 which may be formed of ceramic or refractory material to withstandthe heat of the molten metal without damage. In the dual chamberinduction furnace shown the body is formed with a melting chamber 12which may be relatively large and with a pouring or ladling chamber 14spaced horizontally from chamber 12 and preferably smaller than thelatter. Both chambers are adapted to-contain molten metal 16 and may beconnected by spaced channels 18 formed in the body 10 and lying belowthe normal level of molten metal in the chambers through which the metalcan flow from the melting chamber to the ladling chamber. 2

Metal in the chambers in heated by means of a transformer primary loop,indicated generally at 20, which is positioned between the melting andladling chambers and is magnetically linked with channels 18. As iswellknown in the art the primary loop 20 is energized to produce a flowof secondary heating current for melting the metal in the furnace.

A pump assembly indicated generally as 22 is positionedin operativerelation with the molten metal 16 in ladling crucible 14. Pump 22comprises a pump chamber 24. which advantageously is formed ofrefractory material.

Pump-.chamber- 24. isl-hollowdand has an elongated body xtending.substantially. below. the... level.v of. moltenme al...

16. An opening 26 is provided at the bottom of pump chamber 24 forenabling the-.molten metal in chamber 14 torseekiitselevelnwithinrpumntchamberz 24:}. Aadiseh'arg manner-281thconnectedate:vpumncchamber: 24mand;sis. adapted tocommunicate-withtthe.moltenimetahwithin the pump chamber by =ma X3i:Of.tan :openingmrovided there:

chamber: ,24 is forced. up, throughathedischarge channel 28,-andvout-of,the furnace. The inlet.opening;26 is made: small to dim-it backflow; ofmetal. to; thechamber :14, during this operation.

It: readily will be appreciated thatflwhenrtherpumpchamberispressurizedfor set periods of timethe amount.

of molten metal discharged from, the furnacevaries. in accordance.withthe level of .themoltenmetal in thefur:

nace. amounts ,of molten metal from the. furnace; for each operationofthepump, an electroniecontrol circuitris provided with .the furnace to,automatically compensate for-changes in; level to therebyequalizetheamount of molten. metal discharged from the :furnace,

In accordance with an aspectof'this invention afloat 32,whichadvantageously maybe formedof .a ceramic. material, is-placed insupported position .within pump chamber 24 so astofloaton-themolten-metal 16 therein. A- shaft :34 is connected to thefloat 32 andis adapted to follow the float in accordance, withchanges;in the level of moltemmetal in thefurnacen A'portionof the controlcircuit isprovided within ahousing .36-positioned above thefioat and isadaptedto cooperate with a suitable. electronic; timing circuit, as,described below, to. vary the operatingtimeofi the pump inaccordancewith the level of-moltenmetal 16- asindicated by changesin theposition of. shaft 34; As shown in Figure 2;.and as describedbelowvinzconnectiontherewith, shaft .34 is connected to the wiper 90 ofa potentiometer 86 positioned within housing36- to the endthat-variations in the level of the molten metal within the furnace arecommunicated by the.follQwer-,action of the float 32 and;shaft 34 towiper 90 to thereby causecorrespondingchanges in the positionlofthewiper.

A preferred-embodirnent of the control circuit isshown imFigureiZ ofnthedrawing. The control circuit comprises aytransformer 40 :having .aprimary winding 41 which is conuectedithroughfuse 39 across a pair ofline conductors. 2 .-an d; 43, which,, in turn, are connected to -asource A.- C. supply voltagetnot shown). Onesecondary winding 4410ftransformer: 40 is connected to filaments 45 4 and 46j';of a pair-ofdischarge..-devices 47 and 48, respectiyel-y,;tosupply heater voltagethereto. Another secondar-y winding 49, of transformer 40 is connectedat one end-thereof to the anode 50 of rectifier tube 47 .3.11d at theother end-thereof through a capacitor 51 to cathode 510i rectifier tube47.

Cathode 52 of. rectifier tube 47 is connected to a range andcalibration. network comprising a calibration potentiometer 53 connectedin series with a pair of fixed resistors: 5.4 and 55 and a calibrationpotentiometer- 56. The

contacts of a-range switch 57 are connected across potentiometerv 53 andresistor 54.

Discharge device 48 has its anode 60 'connectedthrough the; windings ofrelay 61 to line conductor 43; Control grid 62 of discharge device 48 isconnected'through a resistor 63 to potentiometer: 56. Screen grid 64 andcathode 65 ofdischarge device 48 are connected through fuse 39-40 lineconductor 42. Cathode'65 also is connected Asitnormally is.desirable todischarge; equalto one terminal of condenser 66, the other terminal ofwhichisconnected to control grid 62.

Condenser 67 is connected between potentiometer 56 and winding 49 oftransformer 40. Resistor 68 is connected in series with contacts 69 and70 of relay 71 across condenser 67. Contacts 72 and 73 of relay 71 areconnected between cathode 65'of discharge device 48 and one terminal ofa bleeder potentiometer. 74.

Potentiometer 74 is connected across the output of a rectifier whichcomprises a transformer 75 having a primary winding 7 6 connected acrossline conductors 42 and 43,, and a secondary winding 77 connected to arectifier bridge network comprising rectifiers 78, 79, 80-and 81. The.output of the rectifier bridge network comprises a filter includingcondensers 82 and 83 and a resistance 84 connected therebetween. Bleederpotentiometer 74 is connected across condenser 83. Wiper 85 ofpotentiometer 74 is connected to a terminal of potentiometer 86, theother. terminal of which is connected to relay contact 73., One terminalof potentiometer 87 is connected to secondary winding 49 of transformer40 and the other termnialis connected through resistance 88 to cathode52 of rectifier 47. Wiper 90 of potentiometer 86-and wiper 91- of,potentiometer 87. are connectedelectrically and the former ismechanically coupled by shaft 34 to fioat32. Thus. wiper 90 is adaptedto be. adjusted inaccordance with the position of the float asdetermined bythe ,level of the; molten metal 16 within ladling chamber14..

Contacts-92 and 93 of initiating switch 94 are con nected between lineconductor 43 and relay 71. Contact 92 of switch 94 also is connectedtoarmature contact 103 of switch; 102 .of relay 71. Contact 104 of switch102 is connected to armature contact 95 of relay 61 and to a terminalofrelay 101. The other terminal of relay 101 is; connected to lineconductor 42. Contact 96 of relay 61 is connected to a terminal ofladling relay 97. The otherterminal of ladling relay 97 is connected toline conductor 42; Pump operating valve 98 is connected at its terminalsto line conductor 42 and at its other terminal to armature contact99 ofladling relay 97. Contact 100 of ,ladlingrelay 97 is connected to lineconductor 43.

In the operation of the control circuit, discharge device 48 normally isbiased to its nonconducting condition"- by bias potentials appliedbetweenits control grid 62 and its cathode=65 from two separate voltagesources.

One bias potential is ,derived'from rectifier tube 47 and is appliedthrough the circuit comprising potentiometer 53, resistances 54-and 55,potentiometer 56 and resistance 63 to the controlgrid. 62' of. dischargedevice 48." A

second bias potential is derived from the rectifier bridge networkcomprising the rectifiers 78, 79, 80 and 81, itsfilter network andpotentiometer 74 and is applied through potentiometer 86uand its wiper90 to wiper 91 of-postentiometer 87;

Wiper, 90 .of; potentiometer 861is mechanically coupled: to ceramicfloat 32 in the pump chamber 24. Thus, as the level ,of molten metal 16in chamber 24 varies, the voltage at; wiper 90 of potentiometer 86varies accordingly and is I added to the voltage at potentiometer 87..The resultant bias voltage on discharge device 48 is the. sum of thesetwo bias potentials and chargescapacitances 66and 59 to apply thisvoltage at cathode 65 of dischargedevice-48 the openingof its normallyclosed contacts 69 and 70 and;

the closing of itsnormally open contacts 103. and 104- The energizationof relay 71 and the subsequent opening of its normally closed contacts69 and 70 initiatesthe. timing cycleof the circuit. Atthistime, however,ladling; relay 97 also is energized th-rough'a circuit including lineconductor 43, initiating switch contacts92 and 93, closed contacts 103and 104 of relay 71, normally closed contacts 95 and 96 of relay 61,relay 97 and line conductor 42. The energization of relay 97 closes itsnormally open contacts 99 and 100 to energize the pump operating valve98 and thereby initiate the pumping of molten metal from the furnace.Advantageously, pump valve 98 may be of the air or gas solenoid typewhereby energization of the valve opens a line to pump chamber 24 topressurize the latter and force molten metal 16 through dischargechannel 28.

The opening of contacts 72 and 73 as a result of the energization ofrelay 101 and the opening of contacts 69 and 70 as a result of theenergization of relay 71 removes the bias potential supplied from therectifier bridge from the storage capacitors 66 and 59. Capacitors 66and 59, which previously had been charged to a voltage representing thesum of the two bias potentials maintains the bias potential on cathode65 of discharge device 48 and holds the latter in a nonconductive state.With contacts 69 and 70 of relay 71 open, capacitor 6! begins to chargeto the value determined by storage capacitor 59. When capacitor 67 hascharged to the 'predetermined bias voltage of capacitors 59 and 66,discharge device 48 starts to conduct and relay 61 in its anode circuitis energized. The energization of relay 61 causes its normally closedcontacts 95 and 96 to open and thereby open the power circuit to ladlingrelay 97. The resultant de-energization of relay 97 reopens its contacts99 and 100 and consequently de-energizes the pump valve 98 to terminatethe pumping action in the crucible.

It will be understood by those skilled in the art that the period oftime defined by the addition of the second bias potential to dischargedevice 48 and the additional subsequent conduction of the latter isdetermined by the amplitude of the second bias potential. Thus, for arelatively large second bias potential, the timing cycle will beconsiderably lengthened, for a relatively small second bias potential,the timing cycle will be correspondingly shorter. The reference time isset by suitable adjustment of potentiometer 87 in the control circuitand this time is varied in accordance with the metal level bypotentiometer 86 coupled to float 32. Thus the amplitude of this secondbias potential is determined by the position of float 32 in pump chamber24 and the length of the timing cycle is varied directly by the level ofthe molten metal in the furnace. When this level is a relatively highone the second bias potential added to the first bias potential is smalland the increase in the timing cycle is relatively short. When the levelof the molten metal is low the second bias potential is correspondinglygreater and the increase in the timing cycle is long. In this mannervariations in the level of the molten metal 16 in the furnace arecompensated for and a uniform amount of molten metal is discharged fromthe furnace for every ladling operation regardless of the level ofmolten metal Within the furnace.

It will be appreciated that the range of the automatic ladling circuitmay be changed to conform with the size of the furnace used by changingthe position of switch 57 in the output of rectifier tube 47 and bysuitable adjustment of potentiometer 87. Potentiometers 53 and 56 arecalibration potentiometers and once set are never changed in position.Additionally, the circuit may be adjusted and balanced by properlypositioning wipers 85 and 91 of potentiometers 74 and 87 respectively.

It will be understood by those skilled in the art that modifications maybe made in the construction and arrangement of the parts of the abovedescribed automatic ladling control means without departing from thereal purpose and spirit of the invention and that it is intended tocover by the appended claims any modified forms of structures, circuitsor use of equivalents which reasonably be included within their scope.

What is claimed is:

1.' A metal melting furnace having means for automa-tically ladling apredetermined amount of molten metal comprising a chamber to hold moltenmetal, a discharge channel disposed in said chamber, pump means forcansing the molten metal to be discharged through said dischargechannel, a float positioned in said chamber such that its position isvaried in accordance with the level of the molten metal therein andactuating means operatively connected to said float and responsive tothe level of the molten metal as indicated by the position of said floatfor causing said pump means to be operated a period of time suflicientto discharge a predetermined amount of molten metal from the chamberregardless of the level of the molten metal therein.

2. A metal melting furnace comprising a chamber to hold molten metal, adischarge channel disposed in said chamber, pump means for causing themolten metal to be discharged through said discharge channel, switchmeans for initiating operation of said pump means, and a circuitincluding a timer responsive to the level of the molten metal in thechamber for automatically terminating the operation of said pump meansafter a period of time determined by the setting of the timer and thelevel of the molten metal.

3. A metal melting furnace in accordance with claim 2 wherein saidcircuit includes storage means for storing a bias potential having anamplitude varying with the level of the molten metal in said chamber.

4. A metal melting furnace in accordance with claim 3 further comprisinga float adapted to be placed in said molten metal whereby its positionis varied in accordance with the level of the molten metal, a source ofpotential. having an output controlled by the position of said float,and means for applying said output to said storage means.

5. A metal melting furnace having means for automatically ladling apredetermined amount of molten metal comprising a chamber to hold moltenmetal, a discharge channel disposed in said chamber, pump meansincluding a solenoid valve adapted to render said pump means operativeupon operation of said solenoid valve for causing the molten metal to bedischarged through said discharge channel, actuating means controlled bythe level of the molten metal for operating said solenoid valve for aperiod of time sufficient to discharge a predetermined amount of moltenmetal from the chamber regardless of.

the level of the molten metal therein.

6. An automatic ladling control circuit for a metal melting furnace ofthe type having pump means associated with a chamber for causing thedischarge of molten metal therefrom comprising a first source of biasvoltage, a second source of bias voltage, a discharge device includingan anode, a cathode and a control grid, means for applying bias voltagesfrom the first and second sources to the cathode and control grid ofsaid discharge device to maintain the latter in a nonconductingcondition, said means including storage capacitance means capable ofbeing charged to said bias voltages and maintaining said bias voltagesupon removal from said bias voltage sources, switch means operative tostart the pump means and to remove the sources of bias voltage from saidcathode and control grid whereby said storage capacitance means maintainpredetermined cathode and grid bias voltages and allow said dischargedevice to remain nonconductive until a desired time cycle has beencompleted, switch means responsive to the conduction of said dischargedevice to stop the operation of said pump means and com trol meansoperative to vary the bias voltage from said second source in accordancewith the level of the molten metal in said chamber whereby the period ofoperation of said pump means is varied by the level of the molten metalin the chamber.

7. An automatic ladling control in accordance with claim 6 wherein saidcontrol means comprises a float adapted to be supported by saidmoltenmetal attsubstantially, theilevelv of. the .latter,;,withinv thechamber.

8.1Anl automatic lladling control in. accordance with claim "7Twhereinsaid second source ofibias potential com: prises a rectifiercircuit having a D.v C.' voltage output, and further comprising aresistance connected to. said rectifier circuit, a wiper adjustablyassociated with said resistance, and shaft means mechanically couplingsaid float to said wiper whereby the voltage at said ,wiper is, variedin accordance with the position of said float.

9. Melting furnace apparatus comprising a chamber to hold molten metal,pump means, operatively associated with said chamber for causingmolten-metal to bedis-r charged therefrom and circuit means forcontrolling the amount of molten material discharged,'said circuit meanscomprising a dischargedevice, means for maintaining said dischargedevice in a nonconducting condition including a source of biaspotential, storage-capacitance means con-. nected to said dischargedevice and-adaptedto be charged to said bias potential, means operativeto initiate operation of said pump means and-to remove said biaspotential source .from said discharge device whereby said storagecapacitance means maintains a bias potential on the discharge deviceuntil the latter is triggered into conduction, and means responsive tothe conduction of said discharge device when said bias applied theretoattains a value more positive thanthe cutfoff potential of theydischarge device for terminating the operation-of said pump means.

10.,Meltingfurnace apparatus a in accordance with claim,9.furthercomprising means responsive to the level of -the.molten.material-.insaid chamber for varying said bias .potentialr whereby the-period ofoperation of said pump ;means, is varied by the level of said moltenmaterial.

1 1.. Melting furnace apparatus in accordance with claim 10 further.cornprisingmeans, for terminating the c0nductionlof saiddischargedevice upon termination of the operation of said pump means whereby saidcircuit means is placed incondition for a further discharge of themolten metal from the crucible.

12. Melting furnace apparatus in accordance with claim 11 wherein.circuit means further comprises adjustable means for. selectivelyvarying the range of operation of said circuit means.

References Cited in the file of this patent UNITED STATES PATENTS465,212 Schilling Dec. 15, 1891 2,244,490 Doyen June 3, 1941 2,397,512Schwartz et al Apr. 2, 1946 2,741,006 Kux Apr. 10, 1956 2,757,326 BoundyJuly 31, 1956

